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Diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), eggs are vulnerable to rainfall, but the impact is dependent on host plant properties and the nature of oviposition sites. The effects of host plants, common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae), and oviposition sites on the fate of eggs subjected to simulated raindrops were investigated in laboratory experiments. In oviposition studies, DBM deposited more eggs on leaf veins than on leaf laminas on both host plants. In common cabbage plants, eggs laid on lower leaves (leaf 2) were less susceptible to dislodgment by rainfall than eggs laid on upper leaves (leaf 6). Eggs laid on the veins on the abaxial surfaces of leaves 2 and 6 of common cabbage plants were less susceptible to dislodgment by raindrops than eggs laid at other sites on this host plant. In Chinese cabbage plants, eggs laid on the veins were less susceptible to dislodgment by raindrops than eggs laid on leaf laminas. When DBM laid eggs in clusters, eggs were less susceptible to dislodgment by raindrops. The presence of waxes on leaf surfaces and concave veins affected egg placement and the retention of eggs at oviposition sites when subjected to raindrops. Eggs were more resistant to raindrops on the concave veined and less waxy leaves of Chinese cabbage plants than on waxy surfaces of smooth common cabbage leaves. When epicuticular wax crystals were removed from common cabbage leaves before oviposition, eggs were more resistant to dislodgment by raindrops. Leaf orientation or angle (horizontal plane vs. an angle of 45°) did not affect the susceptibility of eggs to raindrops. However, eggs were affected indirectly, and vibrations caused by the impact of raindrops resulted in egg removal from both adaxial and abaxial surfaces. Overall, eggs were less likely to be dislodged by raindrops when laid on concave veins and less waxy leaf surfaces. In oviposition tests, DBM laid fewer eggs on plant parts from which they were most easily removed by raindrops, and when they did lay eggs at these sites, they often deposited them in clusters which were more resistant than single eggs to removal by raindrops. The study reiterates the species‐specific nature of DBM‐host plant interactions and shows that female DBM can modify their behaviour to improve the probability of egg survival when substrates available for oviposition are sub‐optimal. [ABSTRACT FROM AUTHOR]

Oviposition patterns of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), differ between common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae) host plants. This study shows that the moth prefers to oviposit on adaxial rather than abaxial leaf surfaces and petioles of both host plants. More eggs were laid in leaf veins than on leaf laminas of both host plants, especially in Chinese cabbage, where 94.6% of eggs were laid in veins. On Chinese cabbage, very few eggs were laid in clusters (≥2 eggs), whereas on common cabbage approximately 30% of eggs were laid in groups of 2 or more eggs. Removal of wax from common cabbage leaves dramatically increased the number of eggs laid singly on the leaf lamina of treated plants, suggesting that leaf waxes affect how eggs are distributed by ovipositing DBM. Eggs were most susceptible to removal by rainfall from the plant surface immediately (<1 h) after oviposition and when close to hatching (>72h old) whereas they were least susceptible 24 h after oviposition. Eggs laid on common cabbage plants were more susceptible to simulated rainfall than eggs laid on Chinese cabbage plants. On common cabbage plants, egg susceptibility to rainfall on different plant parts ranked adaxial leaf surfaces>petioles = abaxial leaf surfaces>stem, but there was no difference in egg susceptibility to rainfall on the various plant parts of Chinese cabbage. Furthermore, on common cabbage plants, eggs laid on both adaxial and abaxial leaf surfaces were afforded significant protection from the effects of rainfall by leaves higher in the plant canopy. On common cabbage plants, oviposition patterns reduce the potential impact of rainfall on eggs, possibly reducing the effect of this important abiotic mortality factor in the field. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: The diamondback moth, Plutella xylostella (L.), is the most widely distributed pest of Brassica vegetables. Control of P. xylostella has relied on insecticides and it has developed resistance to most insecticides. Although research has clarified the resistance status of P. xylostella and the mechanisms of its resistance in northern China, little work has been conducted on long‐term population dynamics in the key vegetable‐growing areas of the region. RESULTS: We reviewed and summarized the history of P. xylostella field management practices in northern China (Haidian, Changping, Xuanhua and Zhangbei). Moths were caught in pheromone traps throughout the cropping season and P. xylostella phenology and the general trends in abundance were analysed using DYMEX modelling software. The initial input in the spring determined population size in all years. The seasonal phenology and variation in abundance in most years and sites were simulated, suggesting that the suitable climate creates the conditions for population outbreaks, and growers' actual management level (spraying and crop hygiene) influenced population abundance. CONCLUSION: Based on climate and using the timing of the initial peak in pheromone trap captures as a biofix, the timing of emergence of the next generation can be forecast, and more effective scouting and regional management strategies against this pest can be developed. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Temporal changes in the pre- and post-alighting responses of mated female diamondback moth, Plutella xylostella L. ( Lepidoptera: Plutellidae), to two species of Brassica ( Brassicaceae) host plants induced by larval feeding were studied using olfactometer and oviposition assays. Females displayed strong olfactory and oviposition preferences for herbivore-induced common cabbage ( Brassica oleracea var. capitata L. cv. sugarloaf) plants over intact plants; these preferences decreased with time and disappeared by the 7th day after induction. In herbivore-induced common cabbage plants, eggs were clustered near feeding damage on the younger leaves (leaves 5-7), whereas in intact plants, eggs were clustered on the stem and lower leaves (leaves 1-4) . However, as the time interval between larval feeding and oviposition increased, more eggs were laid on the lower leaves of induced plants. This demonstrates a change in egg distribution from the pattern associated with induced plants to that associated with intact plants. In contrast, females displayed strong olfactory and oviposition preferences for intact Chinese cabbage [ Brassica rapa ssp. pekinensis (Lour.) Hanelt cv. Wombok] plants over induced plants; these preferences decreased with time and disappeared by the 5th day after induction. More eggs were laid on the upper leaves (leaves 4-6) than on the lower leaves (leaves 1-3) of intact Chinese cabbage plants at first, but the distribution changed over time until there were no significant differences in the egg count between upper and lower leaves by the 4th day post induction. For both host plant species, pre-alighting responses of moths were reliable indicators of post-alighting responses on the first 2 days post induction. The results suggest that temporal changes in a plant's profile (chemical or otherwise) following herbivory may influence attractiveness to an insect herbivore and be accompanied by changes in olfactory and oviposition preferences. [ABSTRACT FROM AUTHOR]

The influence of leaf position and leaf identity on oviposition and neonate feeding site establishment by the diamondback moth, Plutella xylostella ( L.) ( Lepidoptera: Plutellidae), were investigated in laboratory experiments. Leaves were excised from cabbage [ Brassica oleracea L. capitata, cv. Sugarloaf ( Brassicaceae)] and the plants reconfigured on artificial stems made from oasis floral foam. Excised leaves were arranged in their normal (natural) order, in reverse order, or in random order. Relative leaf position, but not leaf identity, significantly influenced the choice of oviposition site; when exposed to female moths, leaves in the lowest three positions always received most eggs. To eliminate the effect of leaf position, oviposition experiments were conducted on excised leaves held at uniform height in individual blocks of oasis foam that had been randomly allocated to a position in a circle at the base of an oviposition cage. Moths laid significantly more eggs on younger leaves, but egg density per unit area did not vary among leaves, supporting the finding that leaf identity did not affect moth oviposition. In experiments that investigated the establishment of neonate feeding sites in reconfigured plants, feeding sites were always concentrated on the youngest two leaves of plants, regardless of their position in normal-, reverse-, and random-order plant configurations. This indicates that leaf identity rather than leaf position determines the site of neonate feeding site establishment. The contrary effects of leaf identity and leaf position on oviposition and neonate feeding site establishment in the same species suggests that different life stages utilize different plant cues (perhaps both physical and chemical) in life stage-specific ways. [ABSTRACT FROM AUTHOR]

Diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), became the major pest of Brassica vegetable production in Guangdong, a province in southeastern China, in the ate 1980s and has continued to challenge growers, particularly during the spring and autumn. Control has relied on insecticides and, as has happened in other parts of the world, resistance to these has evolved and subsequent field control failures have occurred. We review and summarize the history of diamondback moth management in Guangdong. We show that the geographic distribution of the pest in China is well described by a simple climate niche model. Our model predicts the seasonal phenology and some of the variation in abundance among years in Guangdong. Discrepancies may eflect migration and insecticide use at a landscape level. The scale of the pest problem experienced varies with management practices. Local production breaks, and strict post harvest hygiene are associated with lower pest pressure on large-scale production units. As more and more insecticides become ineffective the need to implement an insecticide resistance management strategy, as well as basic integrated pest management practices, will become more pressing. The potential use and development of a better forecasting system for diamondback moth that will assist these developments is outlined. [ABSTRACT FROM AUTHOR]

The development and mortality of diamondback moth, Plutella xylostella (L), were studied in laboratory at 25 ± 1°C, 65& plusmn; 5% RH, and a photoperiod of 16:8 (L:D) h on 10 canola cultivars: 'SLM046,' 'Opera,' 'Okapi,' 'RGS003,' 'Modena,' 'Sarigol,' 'Zarfam,' 'Licord,' 'Hayula420,' and 'Talaye.' Larvae successfully survived on all host plants. The developmental time of immature stages ranged from 15.03 ± 0.15 d on Hayula420 to 16.65 ± 0.29 d on Opera, with a larval period ranging from 7.67 to 8.91 d on these cultivars. Adult female longevity was longest on Hayula420 without any supplemental food. Life table entropy values (H < 6:5) indicated Deevey's type I survivorship curve; however, the value of 0.541 on Hayula420 (H > 0.5) corresponded to type III Major mortality parameters such as fraction of original cohort dying between successive days of age, death frequency (dx) of immature P. xylostella, average daily mortality (μ̄x), and central death rate (mx) were evaluated on canola cultivars and indicated that the highest mx occurred on RGS003, with relatively low potential of population growth, on fifth day of life when the pest is in early larval stages (L1 and L2). The early instars are the most susceptible stages and surfer the highest cause-specific mortality under laboratory conditions. [ABSTRACT FROM AUTHOR]

Constitutive and induced plant resistance against herbivores occurs throughout the plant kingdom, but little is known about the evolutionary relationship between these two types of resistances. We examined the relationships between constitutive and induced resistance to the diamondback moth, Plutella xylostella, in 11 wild species of crucifers, and analyzed the changes in volatiles associated with their expression in two species. We used larvae of P. xylostella and jasmonic acid (JA) as elicitors of the induced response. The level of resistance was estimated as the relative number of eggs laid on the plants by P. xylostella. Substantial variation in constitutive resistance was observed among the 11 crucifer species. When the plants were damaged by larvae, a negative correlation was found between constitutive and induced resistance. However, a positive correlation was detected between constitutive and induced resistance when the plants were treated by JA. The shift in resistance was associated with changes in the emission of volatiles. These results strongly suggest that (1) a trade-off occurs between constitutive and induced resistance in wild crucifers, and that (2) such a trade-off can be observed by treating the plants with a natural, but not an artificial, elicitor. [ABSTRACT FROM AUTHOR]

Surveys for parasitoids attacking larvae and pupae of Plutella xylostella L. (Lepidoptera: Plutellidae) were conducted in the Brassica agro-ecosystem of the Lockyer valley, south-east Queensland between 1999 and 2002. Parasitised hosts were collected from infested plants placed in Brassica crops during the growing season (February–October) and from the natural P. xylostella population on the common weed Rapistrum rugosum L. (Brassicaceae) during the summer production break (November–January). Five species of primary parasitoids were recorded and they ranked in order of abundance: Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae) > Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae) = Apanteles ippeus Nixon (Hymenoptera: Braconidae) > Brachymeria phya Walker (Hymenoptera: Chalcididae) = Oomyzus sokolowskii Kurdjumov (Hymenoptera: Eulophidae). In crops, parasitoids were reared from 23 of the 30 P. xylostella cohorts studied; D. semiclausum was collected at 21 sites, O. sokolowskii at eight sites, D. collaris at six sites, A. ippeus at three sites and B. phya at a single site. The incidence and abundance of hosts parasitised by D. semiclausum increased markedly in winter and early spring months and parasitism rates as high as 95% were recorded. Diadromus collaris and O. sokolowskii were recovered at low levels throughout 2000 and 2001 but parasitism rates never exceeded 11% or 8%, respectively. Parasitism rates are compared with other mortality factors and the contribution that each species of parasitoid makes to the biological control of the pest in the region is considered. Oomyzus sokolowskii has also been reared from P. xylostella collected in Tasmania and Western Australia. This study is the first report of the incidence O. sokolowskii in Australia; however, its wide distribution indicates that its establishment is not a recent event. [ABSTRACT FROM AUTHOR]

Maximizing the contribution of endemic natural enemies to integrated pest management (IPM) programs requires a detailed knowledge of their interactions with the target pest. This experimental field study evaluated the impact of the endemic natural enemy complex of Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) on pest populations in commercial cabbage crops in southeastern Queensland, Australia. Management data were used to score pest management practices at experimental sites on independent Brassica farms practicing a range of pest management strategies, and mechanical methods of natural enemy exclusion were used to assess the impact of natural enemies on introduced cohorts of P. xylostella at each site. Natural enemy impact was greatest at sites adopting IPM and least at sites practicing conventional pest management strategies. At IPM sites, the contribution of natural enemies to P. xylostella mortality permitted the cultivation of marketable crops with no yield loss but with a substantial reduction in insecticide inputs. Three species of larval parasitoids (Diadegma semiclausum Hellén [Hymenoptera: Ichneumonidae], Apanteles ippeus Nixon [Hymenoptera: Braconidae], and Oomyzus sokolowskii Kurdjumov [Hymenoptera: Eulophidae]) and one species of pupal parasitoid Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae) attacked immature P. xylostella. The most abundant groups of predatory arthropods caught in pitfall traps were Araneae (Lycosidae) > Coleoptera (Carabidae, Coccinelidae, Staphylinidae) > Neuroptera (Chrysopidae) > Formicidae, whereas on crop foliage Araneae (Clubionidae, Oxyopidae) > Coleoptera (Coccinelidae) > Neuroptera (Chrysopidae) were most common. The abundance and diversity of natural enemies was greatest at sites that adopted IPM, correlating greater P. xylostella mortality at these sites. The efficacy of the natural enemy complex to pest mortality under different pest management regimes and appropriate... [ABSTRACT FROM AUTHOR]

Field trials and laboratory bioassays were undertaken to compare the performance and efficacy (mortality of diamondback moth larvae) of insecticides applied to cabbages with three high volume hydraulic knapsack sprayers (NS-16, PB-20 and Selecta 12V) and a controlled droplet application (CDA) sprayer. In field experiments, the high volume knapsack sprayers (application rate 500 - 600 L ha  - 1 ) provided better spray coverage on the upper and lower surfaces of inner leaves, the upper surfaces of middle and outer leaves, and greater biological efficacy than the CDA sprayer (application rate 20∼40 L ha  - 1 ). The PB-20 provided better spray coverage on the upper surface of middle leaves and both surfaces of outer leaves when compared with the Selecta 12V. However, its biological efficacy in the field was not significantly different from that of the other high volume sprayers. Increasing the application rate from 20 to 40 L ha  - 1 for the CDA sprayer significantly increased droplet density but had no impact on test insect mortality. Laboratory evaluations of biological efficacy yielded higher estimates than field evaluations and there was no significant difference between the performance of the PB-20 and the CDA sprayer. Significant positive relationships were detected between insect mortality and droplet density deposited for both the PB-20 and the CDA sprayers. [ABSTRACT FROM AUTHOR]

Elevated jasmonic acid (JA) concentrations in response to herbivory can induce wounded plants to produce defences against herbivores. In laboratory and field experiments we compared the effects of exogenous JA treatment to two closely related cabbage species on the host-searching and oviposition preference of the diamondback moth (DBM), Plutella xylostella. JA-treated Chinese cabbage ( Brassica campestris) was less attractive than untreated Chinese cabbage to ovipositing DBM, while JA-treatment of common cabbage ( B. oleracea) made plants more attractive than untreated controls for oviposition by this insect. Similar effects were observed when plants of the two species were damaged by DBM larvae. In the absence of insect-feeding, or JA application, Chinese cabbage is much more attractive to DBM than common cabbage. Inducible resistance therefore appears to occur in a more susceptible plant and induced susceptibility appears to occur in a more resistant plant, suggesting a possible balance mechanism between constitutive and inducible defences to a specialist herbivore. [ABSTRACT FROM AUTHOR]

Field surveys of egg parasitoids of the diamondback moth, Plutella xylostella, were conducted at Redlands and Gatton, south-east Queensland. Eggs of P. xylostella were present all year round in both localities, and parasitized eggs were consistently found between late spring and early winter. Percent parasitism in the range 30–75% was recorded on many occasions, although rates less than 10% were more common. The major parasitoids included Trichogrammatoidea bactrae Nagaraja and Trichogramma pretiosum Riley. Laboratory evaluation showed that the T. pretiosum from Gatton has a high capacity to parasitize P. xylostella eggs under suitable conditions. This study represents the first record of egg parasitoids of P. xylostella from Australia. [ABSTRACT FROM AUTHOR]

Plants are sessile, so have evolved sensitive ways to detect attacking herbivores and sophisticated strategies to effectively defend themselves. Insect herbivory induces synthesis of the phytohormone jasmonic acid which activates downstream metabolic pathways for various chemical defences such as toxins and digestion inhibitors. Insects are also sophisticated animals, and many have coevolved physiological adaptations that negate this induced plant defence. Insect behaviour has rarely been studied in the context of induced plant defence, although behavioural adaptation to induced plant chemistry may allow insects to bypass the host's defence system. By visualizing jasmonate-responsive gene expression within whole plants, we uncovered spatial and temporal limits to the systemic spread of plant chemical defence following herbivory. By carefully tracking insect movement, we found induced changes in plant chemistry were detected by generalist Helicoverpa armigera insects which then modified their behaviour in response, moving away from induced parts and staying longer on uninduced parts of the same plant. This study reveals that there are plant-wide signals rapidly generated following herbivory that allow insects to detect the heterogeneity of plant chemical defences. Some insects use these signals to move around the plant, avoiding localized sites of induction and staying ahead of induced toxic metabolites. [ABSTRACT FROM AUTHOR]

Brassica crops, principally varieties of Brassica oleracea and Brassica campestris, account for over half the total vegetable production in the Democratic People''s Republic of Korea (DPRK). The crops are attacked by a complex of insects and the two major pest species, Plutella xylostella L. (Lepidoptera: Plutellidae) and Pieris rapae L. (Lepidoptera: Pieridae) represent the principal constraints to Brassica crop production. On co-operative farms pests are managed by scheduled application of broad spectrum insecticides and there is no attempt to conserve or utilize endemic natural enemies. The natural enemy complexes attacking P. xylostella and P. rapae in summer white cabbage (Brassica oleracea var. 6–21) on three co-operative farms in the south west of DPRK were studied. The hymenopteran parasitoids Cotesia vestalis Haliday (=plutellae Kurdjumov) (Braconidae), Oomyzus sokolowskii Kurdjumov (Eulophidae) and Diadromus collaris Gravenhorst (Ichneumonidae) attacked P. xylostella while Cotesia glomeratus L. (Braconidae), Cotesia rubecula Marshall (Braconidae) and Pteromalus puparum L. (Pteromalidae) and an unidentified species of Exorista (Diptera: Tachinidae) attacked P. rapae. The generalist epigeal predatory fauna was dominated by Lycosidae (most abundant species: Lycosa t-insignata) and Carabidae (most abundant species: Chlaenius naeviger Morawitz, C. pallipes Gebler, Calathus helensis Schaller). Larval and pupal parasitism rates of both P. xylostella and P. rapae increased during the early summer months but natural enemy exclusion experiments showed that generalist predators were the most important natural enemy guild attacking P. xylostella populations in the agro-ecosystem. In a step towards the development of conservation biological control strategies, field experiments compared current pest management practice with pest threshold based interventions using commercial formulations of Bacillus thuringiensis var. aizawai (Bt). The Bt-natural enemy strategy significantly increased crop yields and the impact of both parasitoid and predator natural enemies on pest populations. However, even under the threshold based Bt regimes, natural enemy impact remained relatively low. The ecology of the major pests and their natural enemies is discussed and recommendations for improved biological control and more effective management of key Brassica pests are made within the constraints posed by current agricultural circumstances in DPRK. [Copyright &y& Elsevier]